This invention relates to a process for clay purification of white mineral oil which has been manufactured using a two-step catalytic hydrogenation process.
White mineral oil ("white oil") is used for a number of purposes. For example, white oil may be used as a plasticizer or as an extender for polymers, as an adhesive for food packaging, or as a caulk or sealant. White oil also may be used as a component in cosmetics and toiletries, such as hand and body lotions, sun care products, lipstick, make-up, make-up remover, cold cream, hair care products, in super fatted soaps and in bath oils.
All of the uses of white oil identified thus far use the oil outside of the human body. Even so, the FDA and white oil manufacturers have rigorous standards that these oils must meet in order to be marketable. The most rigorous standards, however, must be met by white oils which are for internal use in food and pharmaceutical applications, for example, as a laxative or as a binder in pills or tablets, or as an aid in raw food processing.
In all of these applications, white oil manufacturers must remove "readily carbonizable substances" ("RCS") from the white oil. RCS are impurities which cause the white oil to change color when treated with strong acid. The FDA, and white oil manufacturers, have stringent standards with respect to RCS which must be met before the white oil can be marketed for use in food or pharmaceutical applications. In particular, 21 C.F.R. .sctn.172.878 (1988) defines white mineral oil as a mixture of liquid hydrocarbons, essentially paraffinic and naphthenic in nature obtained from petroleum and refined to meet the test requirements of United States Pharmacopoeia XX, pp. 532 (1980) for readily carbonizable substances, and for sulfur compounds.
White mineral oil is prepared from a distillate of petroleum crude oil which has lubricating viscosity and may have been solvent refined and dewaxed or hydrotreated. In the past, various methods have been used to produce white mineral oil from crude oil. The traditional method has been treatment of the distillate with acid. After acid treatment, the white oil was often purified by clay treatment, called contact finishing, to remove by-products that have been created by the acid treatment.
Because it is a problem to dispose of the strong acid waste which results from acid treatment of the distillate, white oil manufacturers have developed new, cleaner methods of white mineral oil production. Applicants' preferred method is disclosed in U.S. Pat. No. 3,459,656, incorporated herein by reference. The process described in U.S. Pat. No. 3,459,656 is a two-step catalytic hydrogenation process. The catalyst used in the first step is a sulfur resistant, non-precious metal hydrogenation catalyst, such as tin, vanadium, chromium, molybdenum, tungsten, iron, cobalt, nickel, and mixtures thereof, present in catalytically effective amounts, for instance, about 2 to 30 weight percent. This first catalyst can be in the free metal or in the combined form, as an oxide or sulfide. The second catalyst comprises a platinum group metal-promoted catalyst, such as platinum, palladium, rhodium, or iridium, present in catalytically effective amounts, generally in the range of about 0.01-2 weight percent, preferably 0.1 to 1 weight percent. The platinum group metal can be present in the metallic form or as a sulfide, oxide or other combined form.
Unlike white oils created by acid treatment, this two-step catalytic hydrogenation process normally produces white oils which do not need further treatment in order to meet the stringent FDA and internal manufacturing specifications required of such oils. Occasionally, however, a batch of white oil is produced which appears to degrade rapidly, resulting in an unacceptable RCS content. The content of the RCS found in this "off-spec" white oil manufactured using catalytic hydrogenation was not clear; however, it was clear that the content was different than that associated with white oil manufactured using acid treatment.
Previously, manufacturers would try to salvage this high RCS oil by re-treating the oil using the two step catalytic hydrogenation process. Or manufacturers sold the oil to customers under a less stringent specification. Either route was costly and/or time consuming.